function update_city_select(){
  var prefecture_id = $('prefecture_id').value;
  var isMSIE = /*@cc_on!@*/false;
  new Ajax.Request(
		   "/bman3/ajax/cities/" + prefecture_id + "?ie=" + isMSIE,
		   {
		     method: "get",
		     onSuccess: function( request ){
		       document.getElementById('city_div').innerHTML = request.responseText;
		     }
		   });
}